Progress in imaging

The first December 2000 issue of TIME Magazine featured a series of articles entitled “Inventors and Inventions of the Year”; in one of them, the ‘winning combination’ of positron emission tomography (PET) and computerized tomography (CT) was celebrated as the major creative achievement in the Medical Science area. While the former method can reveal subtle metabolic processes such as tumour growth, the latter shows anatomical details at a very high resolution. The wining combination now allows the precise location of e.g. a tumour in relation to an organ. By early next year, the new machines will be installed at Manhattan’s Memorial Sloan-Kettering Cancer Center and other prominent medical facilities (TIME, December 4, 2000).

There are more imaging news to come. Surgeons could soon be manipulating 3D moving images floating in mid-air rather than on computer screens, twisting a brain scan around to locate an injury, say engineers at DERA, Britain’s soon-to-be-privatised defence research lab ( DERA says it plans to have its first products based on advanced computer generated holography (CGH) on the market in 2003. Unlike stereography or virtual reality, CGH doesn’t require a headgear to see the image – users manipulate images using tools that exist partly as real objects and partly as virtual tools.

CGH is based on the same principle as the holograms invented by Dennis Gabor in 1949. A hologram is essentially an interference pattern generated from the object being depicted. When light strikes the hologram it is diffracted, forming a series of wavelets. Interference between these wavelets produces wavefronts that simulate the light that would have come from the original object.

In a normal hologram, the image appears to be “inside” the hologram that’s producing it. But with a computer generated hologram it is possible to produce interference patterns that simulate the waves from an object hanging in empty space. This means an image can be projected in front of the screen. There is a another key difference, too: as well as displaying images of real objects, the CGH system can create 3D images of imaginary objects.

The main problem with previous computer-generated holograms has been that they don’t have enough pixels to produce an image of a useful size; roughly a billion pixels are needed to produce a 3D image. DERA developed the screen on which the hologram is formed. Called an “active tiling modulator”, it uses ferro-liquid crystals to create vast numbers of pixels that form a hologram. The system is modular and can be scaled up or down to the required image size.